Minnesota Vikings NFL football running back Adrian Peterson does a running exercise around a large hoop during media availability, Wednesday, May 9, 2012, at Winter Park in Eden Prairie, Minn. Peterson is progressing ahead of pace through his left knee rehabilitation. He tore the anterior cruciate and medial collateral ligaments in a game Dec. 24, 2011. (AP Photo/Star Tribune, Renee Jones Schneider)

The Vikings were running sprints during one of their workouts a couple of weeks ago, and Adrian Peterson was watching off to the side.

Salivating like a kid asking his dad if they can stop for ice cream on the drive home, Peterson turned to head athletic trainer Eric Sugarman.

"He had a look on his face like, 'I know what you want to do,' " Peterson said.

Permission granted, Peterson took the brace off his left knee and jumped in line with the rest of the running backs and wide receivers.

"I finished in first place," he said.

Roughly four months into his post-surgical rehabilitation from the torn anterior cruciate and medial collateral ligaments he sustained in a game last Dec. 24, Peterson is still plenty fast. He's exercising without pain or problems and ahead of the average pace for this injury recovery.

That doesn't mean he's assured of being in the backfield when the Vikings start the regular season Sept. 9, no matter how determined his mind or how supernatural his body might be.

"I'm not going to say with certainty that Adrian is going to play in our first game," Sugarman said. "That wouldn't be fair to me to him or to this organization. That's a long way off from now, and we certainly have a long road to get to that point."

Peterson, though, left no doubt. One of the most optimistic and confident players in the NFL, Peterson said he's set on playing from the start - and not in a limited role. "Full throttle," was his prediction.

"I'll be disappointed if I'm not," Peterson said.

So the Vikings must be able to find the balance between caution toward their franchise player's long-term health and acknowledgment of Peterson's unique healing ability and physical skill.

Hargrove said he hoped the NFL would not discuss the signed declaration publicly and that the league "grossly mischaracterized" his words, which made the declaration a "hot item" that was subsequently leaked to media.

Hargrove's sworn declaration explains how ex-Saints defensive coordinator Gregg Williams and current assistant head coach Joe Vitt told him to deny the existence of a bounty program in New Orleans when he was interviewed by the NFL in March 2010.

Cowboys' cap challenge: The Cowboys have filed a brief in their challenge of a $10 million salary cap reduction by the NFL. Owner Jerry Jones says his team followed the rules before being penalized.

A hearing is set Thursday before arbitrator Stephen Burbank on appeals by the Cowboys and the Redskins, whose cap was reduced by $36 million. The two NFC East teams were penalized for overloading contracts in the 2010 uncapped season despite league warnings.